Fentuz

Hi all,

I tend to ride gravel trails, single XC tracks. My bike is a larger clearance carbon frame fitted with rival shifters and brake calipers (sintered pads); the rest is XC eagle components, E13 wide range cassette, 650B wheels with XC hubs fitted with XC tyres (Vittoria Barzo and Conti XKing/RaceKing). I am between 65 and 70 Kg depending of how close Xmas is. Between the bike, repair gear and myself, the brakes have to stop roughly 80kg.
Last summer, I rode a XC trail (55k) with a fair amount of gradient changes (10 to 20%) and although the bike had been serviced a week before by a Sram specialist, I run out of brakes, they became spongy after several steep down hills.

So, I decided to move to bigger discs to gain better torque and cooling. I ordered both Peak Torque adaptors, front and rear and a set of shimano XT 180 rotors (ice tech thingy). Both adaptors are designed for Shimano Caliper.
https://peak-torque.com/collections/all


these pictures above are from the peak torque website

The front kit is an adaptor plate that comes with 2 sets of screw/bolts. The countersink Torx allows the plate to be mounted on the fork. The 2 other M5 bolts allow the mounting or the 160mm caliper onto the adaptor. This works well of Shimano calipers however, for Sram, it is not the case as the bolt head interferes with the caliper housing. Again, this was designed for shimano and I was aware prior purchase that some tweaks may be necessary. This is not a dig at Peak Torque.
My simple solution was to see if it works with a button head bolt and it did...


You can see my finger pointing at the area the cap head bold interfered with. Nothing to worry about (a little bit of paint and it is all gone )

Now, the issue with the button bolts is the 3mm Hex driving feature that can get damaged easily ( poor seating, over torque etc.) which is a concern Peak Torque has too. I swap these std M5 button bolts for some spare Shimano bolts supplied with rotor. I chose these because they obviously fit, they are shimano certified and are T25 Torx which is what the standard fittings are. Which the Correct hardness, corrosion property and T25, they can be fitted to specified torque without issue.


The rear is a replacement of the 140/160 plate. Again, this is for shimano and required a few tweaks for SRAM. The Sram countersink bolt did not fit; outer diameter too large. So I got M5 countersink 10.9 T25 bolts which were also too large. Nothing to worry about, I fitted them in the drill and run the head on a file (like a reverse lathe) and turned down the head et voila... It all fitted together.

But, Planet X had a sale and I could not resist a set of fulcrum 650B for £129... perfect winter wheelset with cheaper Shimano SLX rotors... once fitted, I noticed the rotor fins were catching on the caliper housing. May be the frame tolerance and brake line makes this assembly too tight so, I fitted two stainless steel washers between the frame and the plate. The washers cover the overall frame location points. As everything is in compression and flush, I am not worried about micromotion issues. And yes, I use blue loctite.

So this is for the assembly but, how does it feel after 1000kms?

I rode mostly with the WTB/specialized Wheelset fitted with XT rotor and the braking is more crisp when I apply the brake. The performances are much better and immediate. Is it due to the ice tech rotor design Vs SRam Centerline Rotor, I cannot say. But, started to ride with 180 at the front first (100kich) and the improvement was very noticeable.
When I went for 180 front and rear, I noticed that the rear bake used on its own worked better.
When I applied both, It is a bit better than 180/160.

I did not notice any difference between XT ice Tech and SLX ice Tech rotor performance. So far, I think the only difference is the weight.

So, when used to the limits, I think this is a good upgrade especially if you consider the alternatives: Hope 4 pistons (or hope 4 piston +20mm) or Columbus new fork with 180 mounts.
Now would I advise 180 front and rear? If you look at XC MTB spec, they tend to be 180 front 160 rear so considering price Vs performance, I think a 180 front with a premium rotor and a rear 160 premium rotor might be the best cost effective option vs performance:

Front peaktorque adaptor with 180 icetech rotor (or similar) and rear 160 icetech rotor (or similar). Much easier and cheaper conversion for the money.

So why am I keeping the 180 at the back other than the fact it is already fitted. I am missing the last phalanx on my left index so, grabbing the brake lever and pull harder is not easy with 1 cut finger. With the 180 on the rear, I have more torque available and I find it easier. I would suspect this would be an advantage for people with the same issue.
I guess it would be good for heavier riders too.

freetors

Interesting to hear your thoughts on this. My salsa cutthroat is apparently designed to run 180 rotors with the right adaptors but I haven't done it yet. Honestly I'm pretty amazed at the reluctance of drop bar people to big rotors. The weight increase is trivial but the increased cooling and lower force required at the lever is very welcomed.

Koyote

I've ridden and raced gravel in the PA/OH/WV region with plenty of climbing (>100ft per mile) and commensurate descents...plenty of long descents at the grades described by OP. My Ultegra disc brakes with 160mm IceTech rotors and resin pads have always performed more than sufficiently -- which leads me to believe that the OP's problem was with his equipment and/or setup, and not with the rotor size.

tyrion

I'm a fan of big rotors. (I am a big guy, 229.9 lbs.) 203mm in the front, 180mm in the rear. Resin pads. Extra braking leverage for an extra 50 grams? I'll take it.

Resin pads for the smoothness and quiteness, big rotors for the leverage.

Fentuz

like i said, the bike had been serviced by a sram specialist who did all the bleeding etc. unless Sram centerline are crap rotors (which they are not)….
i was riding while a XC rider who races in the French XC championship, this was not a gravel, it was 90’s XC

Germany_chris

I'm also a fan of big rotors I just don't see a downside.

Koyote

You described the brakes as becoming "spongy," which suggests air in the brake lines.

Fentuz

not quite, it was over heated fluid as the disc, pads and caliper housing were too hot. Once it cool down, it worked again.

msu2001la

The difference in weight seems trivial to me. Looking at XT centerlocks:
140mm= 88g
160mm=108g
180mm=132g

It's also worth noting that the Shimano road rotors are actually a bit heavier. I'm guessing because they have larger cooling fins? The Ultegra centerlock rotors are listed as:
140mm= 108g
160mm= 128g

I've never understood why anyone runs 140mm rotors. On the flip side, I'm north of 75kg and have never felt like 160mm rotors were problematic, but if I were barreling down mountain descents I could see wanting to try 180mm.

rosefarts

I think you upgraded the wrong component. I’m 5lbs lighter than you. Fairly close.

I had those brakes and I definitely ran out of brakes on big descents with a 160/140 pairing. And with those super straight brake levers, I just couldn’t grab well.

I switched to Archer Trail shifting and to do it, I needed TRP Hylex. The difference is dramatic. Both in ergonomics and in quality of brakes. Incidentally, I haven’t even changed my rotors.

I’ve got 2 180’s my MTB, it’s awesome. I’m sure that would stop a gravel bike. I think SRAM makes bad brakes though.

Fentuz

I’m not really sure that spending over $400 is quite comparable to £120. if I wanted to do so, I would go Hope 4 pots which at least allow shifting unlike trps….


today, i did a usual ride and I found that this new setup is more ON/OFF (per sintered pad description actually), it allows me to stab the brakes shortly and release smoothly to reduce speed promptly and later while keeping good grip.
while I am aware this is not to everybody’s liking, this is how i learnt to brake racing on track with pro drivers and this technic works for me….

if further proof was needed, I bagged 2 more KOMs…

rosefarts

You having Hope calipers is a crucial detail. I must have missed that earlier. That makes it a lot harder to just blame the sub par Sram calipers.

Ill betcha that I’m shifting faster and with less effort than you are. But it wasn’t a cheap option.

Fentuz

No, I do not have Hope calipers (yet), I miss spelled. I meant to say: "if I wanted to spend ~$400, I would go for hope calipers". Like I said, I think the better setup would have been:
-> Front: 180adaptor + icetech 180rotor (SLX)
-> Rear icetech 160 rotor (SLX)
For ~£75-80 or ~$100

Again, far from the $400 caliper upgrade.


On the separate note, the sram Rival/Force calipers are not bad; they just need a clean up very so often to avoid potential jamming. Nothing different that the AP twin pots I had on my race car.

Badger6

I don't disagree with this statement. Not even a little.

This has nothing to do with your brakes, friend!

Fentuz

Better braking performance does help; it allows to brake later and better which in turn improves the overall time.

When I go down a 1.5m wide track in between ferns @30-40kph with loose surface corner ot blind corner, making sure the speed is in line with available grip is important. If I have to drag on the brake longer to decelerate then, I will be slower that a quick stable. The bike remains stable and back on the gas passed the apex.

dwmckee

Hah, +2!